Lead-copper-silver alloys and process for producing same



LEAD-COPPER-SILVER ALLOYS AND PROCESS FOR PRODUCING SAME Raymond E. Hammeras, Whittier, Calif., and Elver F. Bowalish, Tacoma, Wash.,-assignors to Bowdish and Associates, Inc., Los Angeles, Calif., a corporation of California No Drawing. Continuation of application Serial No. 221,939, April 19, 1951. This application November 3, 1954, Serial No. 466,688

20 Claims. c1. 75-166) This application is a continuation of our copending application, Serial Number 221,939, filed April 19, 1951, now abandoned.

This invention relates to an improved method of producing lead alloys and particularly alloys of lead with copper; although the method is equally well adaptable to alloys of lead with silver or of lead with both copper and silver.

Alloys of these metals wherein there is a high lead content are desirable, particularly for use in connection with friction surfaces which are subjected to bearing pressure, for the well-known reason that the lead acts as a lubricant. This is especially true When the bearing surface must function with a relatively small amount of lubricating oil or grease present; and all the more so in the total absence of lubricating oil or grease, as in socalled dry or self-lubrication. An optimum lead-copper or lead-silver alloy for 'such use is one wherein the lead content approximates 50%, the other 50% being comprised entirely of copper or of silver.

As is also Well known, the great difference in the melting and boiling points in these two metalslead and copper or lead and silver-creates an inherent difliculty in attempts to blend the two molten metals together, for the reason that much of the lead is lost through vaporization during the mixing or stirring of the molten mass. In attempts to overcome this difliculty, resort has been had 'to various slags or fluxes which float in molten state on the surface of the mixture to serve as a blanket to retain the lead in the mixtures. With the fluxes and the methods heretofore employed, some degree of success toward a high lead content alloy has been attained, even to the extent of obtaining a lead content of 50% or higher.

Invariably, however, segregation of the lead is encountered and the problem has long been to overcome this segregation so as to produce a completely uniform blend of the lead and copper (or lead and silver). In attempts to overcome this segregation, resort has usually been had to the use of small amounts of some third element in the mixture, such as sodium, lithium, telluriurn, selenium, cadmium or tin. This practice, however, does not produce a purely two-element blend or alloy, for the' reason that the presence of the third element persists throughout the process and in reality gives a three-element product.

Thus while mixtures of lead and copper and of lead and silver have been obtained in the prior processes with a high lead content, such mixtures have generally been attended with lumpiness, due to segregated lead particles throughout the alloy and a problem long confronting the industry has been to obtain a uniform blend of the lead in the copper or silver throughout the entire mass of the alloyed product while keeping the content of the lead well up toward the 50% point or higher. Ordinarily, in the case of lead and copper, uniformity ceases when the lead content exceeds 23% and it has been reported that if the copper is melted first and the lead 2 dropped into the melt, no amount of stirring will result in a melt which is of uniform composition throughout and the first castings out of the crucible may contain as little as ten per cent of lead. When a non-uniform leadcopper alloy is employed in friction surfaces subjected to heavy bearing pressure, and particularly in instances where self-lubrication is desired, the lubricating characteristics of the lead cannot'be utilized to its greatest advantage, so that these non-uniform lead-copper and lead-,

silver alloys are poor materials for friction surfaces which are subjected to heavy bearing pressure.

Another difliculty which has attended alloys of lead I with copper or silver as they have been produced heretofore is the fact that when the alloy is heated to or above the temperature of the melting point of pure lead (in the neighborhood of 621 F.) the lead begins tomelt and separate from the copper or silver. This characteristic of the prior art alloys has made it extremely diflicult, if not impossible, to employ them as high heat bearings and on high heat frictional. surfaces.

It is an object of this invention to produce a leadcopper or lead-silver alloy with a lead content of from 30 to 70 per cent wherein the lead will be uniformly blended throughout the entire mass of the alloy, thereby giving a completely homogeneous mixture.

Another object is to overcome the segregation of the lead in the production of high lead content copper and silver alloys without the use of a third element, metallic or otherwise, in the blend.

Another object is to produce a lead-copper and leadsilver alloy in which the lubricating qualities of the lead are fully retained, thereby giving a superior preparation for use where self-lubrication is necessary.

Another object is to produce a lead-copper or leadsilver alloy of high lead content that will withstand temperatures in the neighborhood of 1,000 F. above the melting point of pure lead without suffering the melting out and separating of the-lead from the copper or silver.

Another object is to provide an improved flux to be used in a bath of molten metals in the production of Per cent Hematite ore to 98 Silicon dioxide A to 2 Ammoniumchloride A to 5 Sodium carbonate A1 to 3 When the sodium carbonate is not used, it should be replaced with an equivalent amount of ammonium chloride. To some extent the ammonium chloride may be. replaced by sodium carbonate, but the ammonium chlo.- ride should not be entirely replaced by the sodium carbonate. We prefer to use these ingredients in the following proportions:

Per cent Hematite ore 94 Silicon dioxide 2 Ammonium chloride 2 Sodium carbonate 2 They are ground to a fineness of 50 to mesh and thoroughly mixed before use.

In the production of our alloy of 50% lead and 50% copper, weprefer to first introduce into a clean crucible Patented May 1, 1956 an amount of charcoal equal to approximately 1.5 pounds for each 100 pounds of the finished alloy. It is preferable to use aerated charcoal. It is also preferable that a portion, about one-half, of this charcoal be added to the empty crucible and the remaining part added after the copper is placed in the crucible. After the charcoal is placed in the crucible, the entire amount of copper to be used in the batch is added and the copper is then covered with the above described fiux. The mixture is then heated until the copper is melted and brought up to a temperature which may range from 1800 F. to from about 2500 F. to 2600 F. We prefer to bring it to a temperature of around 2350-2400" F. The amount of flux may vary from about 1 pound to pounds per 100 pounds of alloy, 3 pounds being a preferred amount. At this point in the process we begin to add the lead to the mixture. It should be cut into pieces preferably of not more than pound in weight. The lead is preferably introduced in successive stages, about 20% of the total amount of lead being used for each stage. Each batch of lead is added while stirring the copper vigorously with a pre-heated stirring rod. During and after the addition of each successive batch of lead, the mixture is heated until the temperature again reaches 2350-2400 F. It is desirable that the temperature should not drop below the lower limit of the above mentioned range, preferably not below 1900- 2000 F. After the final batch of lead is added, the temperature of the mixture is raised to around the upper limit of the range mentioned above, preferably to around 2400 F., and held at that temperature for a short period of time, say 5 minutes, the mixture being stirred vigorously all the while. The slag is then skimmed off and the alloy poured into open moulds.

In order to allow for loss through oxidation and evaporation, about 2% more lead than copper should be used. In order to insure a perfectly homogeneous mixture, the alloy from the above described procedure should be remelted. In doing this the alloy is again covered with the above described fiux, using about the same amount as was employed to cover the copper before the introduction of the lead. In this remelting step, the alloy and flux are heated to substantially the same final temperature as that employed during the formation of the alloy described above, the molten alloy being again stirred vigorously all the while. After skimming the slag, the temperature may be allowed to drop to between l700-l900 F. before pouring. This characteristic of becoming improved upon remelting is in contrast to that which commonly prevails in lead-copper and lead-alloys wherein the tendency has been for the lead to segregate out upon remelting.

This process is equally well suited for the production of lead-silver alloy, and in the process as described silver can be substituted for copper and the process carried out in substantially'the same manner. As in the case of our lead-copper alloy, the lead-silver alloy produced by this method has been found to be of superior quality, particularly in that the lead is completely uniformly blended with the silver throughout the entire mass, thereby giving a completely homogeneous mixture, and that in turn permitting the lubricating qualities of the lead to be utilized to the greatest extent when the alloy, whether it be lead-silver or lead-copper, is used in connection with a friction surface subjected to bearing pressure, and especially in instances where selflubrication is desired or is necessary.

We have found that this homogeneity of mixturesfreedom of lumpiness and the like due to the absence of segregation of the lead-maintains by our process for copper and for silver alloys where the lead is as high as 70%, the other 30% being copper or silver without the presence of any third element or ingredient in the alloy. The process is equally suitable for these alloys when it is desired to drop the lead content to as low as 30 percent.

Over and above this characteristic of the lead making a completely homogeneous mixture or blend with the cop- .45. per or silver throughout the entire mass, our alloy has the outstanding characteristics that the lead will not melt and separate from the copper or silver when the alloy is subjected to heat at and above the temperature of the melt ng point of pure lead. Thus we overcome a difficulty which attends the lead alloys of copper and silver heretofore produced. By tests we have found that in a 50% lead and 50% copper alloy the lead is not released until the temperature reaches above 1600 F. We have found that this characteristic does not attend when the prior-art fluxes are employed and believe that our flux causes the copper to solidify before the lead in a manner whereby the minute lead particles become encased in small surrounding frameworks of copper. Whatever may be the reason for this extremely important characteristic, the fact that our alloy will withstand such high temperature without melting and separation of the lead makes it highly advantageous for use, either as a bearing metal or on frictional surfaces where high heat is encountered, and particularly where self-lubrication imparted by the lead must be relied upon.

As evidence of the beneficial influence which our flux exerts in the process of alloying lead with copper or silver, we have found that by taking a lead-copper alloy such as those produced by prior-art methods wherein the lead is not blended uniformly throughout the mass, but is partially segregated, and remelting it in the presence of our flux a material improvement in the quality of the alloy results, in that the lead is more uniformly blended throughout the mass, there being a less amount of the segregated lead.

We have likewise found the process adaptable for the alloying of lead with both copper and silver in the same alloy to give a completely homogeneous mixture, with a high lead content; for example, a copper-silver-lead alloy having 30 to 70 percent of lead, the copper ranging from 25 to 44 percent and the silver from 25 to 6 percent. Other metals, such as nickel, chromium and tin, in quantities ranging up to 10 percent in the final alloy, can be alloyed with our basic alloy (lead-copper) by first alloying the copper with the other metal, in an open crucible at a temperature of 300 F. above the melting point of the copper or of the other metal, whichever is the higher, and then using this copper alloy in place of the copper in the method hereinabove described for the alloying of lead and copper.

The superior quality of the lead alloys of our process makes them especially useful in powdered form in resins for forming a self-lubricating coating on friction surfaces; in powdered and chipped form in frictional compounds and mixtures for brake linings and clutch facings and the like; in powdered form in resins for forming heat and electrical conducting coatings on various surfaces, or for coatings on electronic tubes to conduct heat away from the tubes and to shield them from interference; and for non-corrosive coatings on various surfaces.

The alloy of this process is also a superior material for use as an additive to brake block material before the material is moulded into brake blocks, the alloy being chipped to a fineness of from 0 to 60 mesh and thoroughly mixed with standard brake block materials.

When using our alloy for the above-mentioned coatings we first grind it to a fineness of from 200 to 900 mesh. It is then mixed with a resin, such as the standard resin manufactured by various firms, in amounts which may range from one-eighth pound up to ten pounds of the powdered alloy per gallon of resin, depending upon the thickness of film of alloy desired. Subsequent applications of the coating may, if desired, be added to increase its thickness. A resin thinner may be used to dilute the mixture to a desirable consistency when spraying it onto the surface to be coated. After the surface is coated with the mixture it is baked in an oven at a temperature of from 300 to 500 F. The thickness of the coatings may vary from .0005 inch on fine gears and the like to about .005 inch on brake shoes and other parts where the tolerances are not so critical.

It will be understood that the examples and details of our invention given hereinabove are exemplary in nature and that various changes and modifications may be made thereto by those skilled in the art without departing from the spirit of our invention, and that there is comprehended within our invention such modifications as come Within the scope of the following claims.

We claim:

1. The process of making a substantially completely homogeneous alloy of lead and copper, which comprises introducing lead into a mass of molten copper which is covered with a protective flux consisting essentially of hematite ore, and stirring the mixture vigorously while applying heat until the temperature of the mixture is raised to approximately that of the molten copper prior to the introduction of the lead.

2. A process in accordance with claim 1 wherein the hematite ore has admixed with it A% to 2% by weight of silicon dioxide and A% to 5% by weight of ammonium chloride.

3. A process in accordance with claim 1 wherein the hematite ore has admixed with it /4% to 2% by weight of silicon dioxide, to 5% by weight of ammonium chloride and to 3% by weight of sodium carbonate.

4. The process of making a lead-copper alloy which comprises heating a mass of copper in the presence of a flux consisting essentially of hematite ore until the molten copper attains an initial temperature of from 1800 to 2600 F., then adding lead in successive increments while the mixture is undergoing vigorous stirring, bringing the temperature of the mixture after the addition of each of said successive increments of lead back to the said initial temperature of the molten copper and after the final increment of lead is added holding the temperature of the mixture at the said initial temperature for a period of time and subsequently cooling the mixture.

5. A process in accordance with claim 4 wherein there is admixed with the hematite ore to 2% by weight of silicon dioxide and 4% to 5% by weight of ammonium chloride.

6. A process in accordance with claim 4 wherein there is also added to the molten copper, prior to the addition of the lead, charcoal in an amount equal to /2 to 3 pounds per 100 pounds of alloy.

7. A process in accordance with claim 4 in which there is added to the copper charcoal in an amount equal to V2 to 3 pounds per 100 pounds of alloy and wherein the hematite ore has admixed with it A% to 2% by Weight of silicon dioxide and to 5% by weight of ammonium chloride.

8. A process of making an alloy consisting essentially of lead and a metal selected from the group consisting of copper and silver which comprises heating and agitating a molten mixture of lead and the metal selected from said group under a protective flux composed essentially of hematite ore until the temperature of the mixture is raised to from 1800 F. to 2600 F.

9. A process in accordance with claim 8 wherein the hematite ore has admixed with it from V4% to 2% by weight of silicon dioxide and from 1, to 5% by weight of ammonium chloride.

10. A process in accordance with claim 8 wherein the hematite ore has admixed with it from 4% to 2% by weight of silicon dioxide, to 5% by weight of ammonium chloride and /4% to 3% by weight of sodium carbonate.

11. A process of making an alloy consisting essentially of lead and a metal selected from the group consisting of copper and silver, and in which the lead content of said alloy is from 30% to which comprises heating and agitating a molten mixture of lead and the metal selected from said group under a protective flux composed essentially of hematite ore.

12. A process of making an alloy consisting essentially of lead and at least one metal selected from the group consisting of copper and silver which comprises heating and agitating a molten mixture of lead and the metal or metals selected from said group under a protective flux composed essentially of hematite ore until the temperature of the mixture is raised to from 1800 F. to 2600 F.

13. A process in accordance with claim 12 wherein the hematite ore has admixed with it from A% to 2% by weight of silicon dioxide and from to 5% by weight of ammonium chloride.

14. A process of making an alloy consisting essentially of lead and at least one metal selected from the group consisting of copper and silver, and in which the lead content is from 30% to 70%, the copper and silver, when either is the only metal selected from said group, comprising the remainder of said alloy and the copper and silver, when both are selected from said group, being respectively 25% to 44% copper and 6% to 25 silver, which comprises heating and agitating a molten mixture of lead and the metal or metals selected from said group under a protective flux composed essentially of hematite ore until the temperature of the mixture is raised to from 1800" F. to 2600 F.

I 15. A process of making an alloy consisting of approximately 30% to 70% of lead, 25-44% copper and 625% silver, which comprises heating and agitating a molten mixture of the said metals under a protective flux composed essentially of hematite ore.

16. A process in accordance with claim 15 in which the hematite ore has admixed with it from 4% to 2% by weight of silicon dioxide and from A to 5% by weight of ammonium chloride.

17. A lead-copper alloy in which the lead content is from 30% to 70% and which is substantially completely homogeneous, which undergoes substantially no segregation of the lead upon remelting and which gives superior self-lubrication when used as a frictional bearing metal, produced by subjecting the metals in molten state to the influence of a flux consisting essentially of hematite ore admixed with to 2% by weight of silicon dioxide and A to 5% by weight of ammonium chloride.

18. A lead-copper alloy in which the lead content is from 30% to 70%, and which is substantially completely homogeneous, which undergoes substantially no segregation of the lead upon remelting, produced by subjecting the metals in molten state to the influence of a flux consisting essentially of hematite ore.

19. A copper-lead'silver alloy consisting of 3070% lead, 2544% copper, and 625% silver, characterized by the lead being uniformly distributed throughout the mass to give a substantially completely homogeneous mixture, and by the lead not segregating upon remelting.

20. A flux for use in producing an alloy of lead and a metal selected from the group consisting of copper and silver, consisting essentially of hematite ore admixed with to 2% by weight of silicon dioxide and to 5% by weight of ammonium chloride.

No references cited. 

14. A PROCESS OF MAKING AN ALLOY CONSISTING ESSENTIALLY OF LEAD AND AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF COPPER AND SILVER, AND IN WHICH THE LEAD CONTENT IS FROM 30% TO 70%, THE COPPER AND SILVER, WHEN EITHER IS THE ONLY METAL SELECTED FROM SAID GROUP COMPRISING THE REMAINDER OF SAID ALLOY AND THE COPPER AND SILVER, WHEN BOTH ARE SELECTED FROM SAID GROUP, BEING RESPECTIVELY 25% TO 44% COPPER AND 6% TO 25% SILVER, WHICH COMPRISES HEATING AND AGITATING A MOLTEN MIXTURE OF LEAD AND THE METAL OR METALS SELECTED FROM SAID GROUP UNDER A PROTECTIVE FLUX COMPOSED ESSENTIALLY OF HEMATITE ORE UNTIL THE TEMPERATURE OF THE MIXTURE IS RAISED TO FROM 1800* F. TO 2600* F. 